The advent of highly portable camcorders has enabled moviegoers to wrongfully and surreptitiously capture the video content of movies displayed in theaters. In an effort to combat such activities, some theaters have incorporated systems for preventing recording of movie content or degrading video captured by camcorders. The approaches have varied, but each has attempted to exploit the differences between the optical technology of camcorders and the human optical system. For example, some theaters have employed the use of ultraviolet or infrared light, both of which are invisible to the human optical system but detectable and recordable by typical camcorders. Unfortunately, the use of ultraviolet and/or infrared light to prevent or degrade recording video recording may be easily nullified when a moviegoer incorporates an appropriate spectral filter with his camcorder. Another attempt at preventing video recording is the use of frequency modulation which may deliver, for example, a copyright infringement warning detectable and recordable by typical camcorders as part of video degradation. Unfortunately, the frequency modulation method may introduce a flicker visible to the human optical system which results in an unpleasant viewing experience for the audience.
Where both a theater projection system and a camcorder operate based on the RGB color space, information of the pixel input ([Rl Gl Bl]) to the RGB based projector which is processed by the projector mechanism (MP) may be shown as accurately transferable to the pixel output ([RO GO BO]) of the RGB based camcorder which is processed by the camcorder mechanism (MC). Accordingly, another attempt to prevent unauthorized video recording of movie content was made by introducing an extra primary color (which can involve the use of a second projector) so that different projected spectral combinations can be metamers and can be incompatible with typical camcorders. (In simplest terms, a “metamer” is a color that is different than another color, but yet appears to be the same color as the other to an observer and “metamerism” is the use of metamers such that two or more different colors (i.e. metamers) are perceived as the same color to the observer.) This technique takes advantage of the differing spectral sensitivity curves of the RGB camcorder and the typical human optical system. The addition of the fourth primary color allows the projectionist to display a movie with a spectral combination of four primary colors which are perceived by the moviegoer generally as originally intended by the movie producer because of the nature of metamerism (i.e. there is a plurality of spectral power distributions that will be perceived by the human eye as the same color, but will “result in different values in a video camera” as described in WO 2004/0408989 A2). The use of a second projector may result in synchronization problems with the primary projector. Further, the introduction of only a single extra primary color results in only one-dimensional metamerism which could be the easiest form of metamerism to circumvent through linear, single, or conventional equation solutions.
It is therefore desirable to develop an improved video recording prevention system.